I own a 2001 ford expedition 4.6 liter vehicle. I am having problems with the heater. The blower works fine but the air is only slightly warmer than the temp outside. I have changed the thermostat, I thought it may be hung open not allowing the coolant to get warm enough, but that did not fix it. Do you think there may be a blockage in the line to the heater core? There are no coolant leaks to be found. Thank you fro your time,
With the engine cold. Drain antifreeze. Disconnect the two lines that go to the heater core. Mark which one goes where. Then use a hose and back flush the heater core. When you see a lot of junk comming out of the other hose then run the hose until clear. You may want to change directions a couple of times to make sure it is good and clean. If you can't get it to flow free when flushed you may need to have it replaced or professionally flushed. Once running free after flushing reattach hoses. Most auto stores have a kit to flush the system.